Technical Field
The subject matter disclosed is generally related to piping thread forms, in particular 4-round thread forms (i.e., four thread per inch pipe forms).
Description of Related Art
Common piping used in oil pipelines generally feature eight (8) thread per inch (TPI) thread forms, also known as 8-round. This thread form is capable of withstanding high pressures and the associated tensile loads as required by American Petroleum Institute (API) standards. However, eight thread per inch thread forms are prone to cross-threading during installation, especially in larger diameter piping.
Additionally, while hundreds of thread forms may exist, many thread forms appropriate for metal piping, such as a buttress thread, cannot be machined into composite pipes due to issues with chipping and cracking. Issues with chipping and cracking are especially present with the sharp angles of the buttress thread. Similarly, premium threads, a class of high-performance thread types commonly used in modern oilwell and gaswell completions, are available in a number of configurations and are typically designed to provide superior hydraulic sealing, improved tensile capacity and ease of make-up. However, due to the machining issues with composite piping, premium threads also cannot be fully implemented into composite piping.
Accordingly, there is need for a thread form that is less prone to cross-threading during installation and capable of being machined into composite piping, yet still capable of withstanding high pressures and tensile loads.